1. Field of the Invention
This invention relates to a sheet processing apparatus for fetching sequentially sheets on which images are formed by an image forming apparatus such as, e.g., photocopiers, printers, and so on, stapling the plural sheets with a stapling means, and folding the sheets in folio and an image forming apparatus.
2. Description of Related Art
Some image forming apparatus such as photocopiers or the like today can do bookbinding by stapling plural sheets and folding the sheets in folio where connected with a sheet processing apparatus. Such a sheet processing apparatus capable of bookbinding fetches sequentially the sheets on which images are formed at the image forming apparatus body, staples the sheets at about the center of the sheet bundle upon driving the stapler unit, and folds the sheets in folio where the sheets are conveyed to a folding means.
As a structure for folding the sheets in folio, it is structured by a folding roller means made of a roller pair, and a projecting means made of a projecting plate and so on. The projecting plate folds the sheet bundle upon projecting the stapled position of the sheet bundle between the nip portions, and the folded sheet bundle is pressed and conveyed by the roller pair to fold the bundle in folio. Therefore, the sheet bundles delivered to the delivery tray are delivered in a state that the sheet bundles are folded in folio and bound in a book form at the center stapled position of the sheets.
However, in the folding roller means, at least one roller is movable to change the distance to the nip position according to the thickness of the sheet bundle. If the projecting position by the projecting plate is constant, the plate cannot hit the center of the distance between the nips of the roller pair when the thickness of the sheets is deviated. That is, if the sheet bundle becomes thick, the projecting plate hits the center between the nips until the sheet bundle is nipped by the folding roller, but when the folding roller nips the sheet bundle to change the distance between the nips, the plate may hit a position shifted from the center of the distance between the nips, and therefore, the folding position may be shifted due to differentials in loads given to upstream and downstream of the sheet bundles, or wrinkles may occur on the sheet and may cause tears in sheets.
This invention is made with respect to the above viewpoint, and it is an object to provide a sheet processing apparatus in which the projecting means can always hit the center of the distance between the nips as the projecting position even where the distance between the nips of the folding roller is changed.